It is important in radiotherapy treatment of patients to be able to shield portions of the body, such as vital organs, from the effect of such treatment, i.e. in the X-ray treatment of lung diseases it is important to shield the heart from such X-rays. In the past this has been accomplished by the use of metal shielding blocks generally formed from a mold made from foam, resinous material, such as polystyrene block, which is provided with a cutout in a pattern corresponding to that of the area of the particular patient which is to be shielded. Thereafter, the patterned opening in the foam block is filled with shielding material such as lead or special purpose alloys thereof. The thus formed composite foam and shield material block is thereafter used as shield means placed between the treatment source and the patient so as to shield the patterned areas from receiving the treatment rays. Such radiotherapy shielding blocks are presently formed by an apparatus including a lighted table on which an X-ray of the particular person to be treated is placed. Above the table is a platform for retaining a styrofoam block. A frame is provided from which an electrically heated wire is suspended and heavily counterweighted in order to maintain the wire taut. The other end of the wire has a pointer for manually tracing the X-ray exhibited on the lighted table. As the pointer is manipulated to trace the particular section or sections of the X-ray which are to be shielded from the treatment rays, the heated wire automatically cuts a corresponding pattern from the styrofoam block which is mounted above the pointer and within the path of the wire.
With such device, it is important and necessary that the wire be maintained taut by the counterweight in order to insure that a true pattern will be cut from the block. The operation must thus continually work against the counterweight, it being understood that the wire passes over pulleys mounted on the frame whereby the wire may extend as the outline of the X-ray is traced. It is, however, somewhat difficult and fatiguing for an operator to continually operate against such tension during the tracing process, particularly when relatively fine areas are being traced. Furthermore, there is always the possibility that the flexible wire will not cut a true pattern, even though heavily counterweighted. Accordingly, it is desirable to eliminate such operator fatigue while at the same time providing more positive means for maintaining the cutting wire taut to better assure accurate tracing and transmission of the tracing to the block being cut.